Ignitron welder control circuits



1941- w. E. PAKALA 2,265,000

mun'nou WELDER CONTROL'CIRCUITS Filed Feb. 16, 1940 wnmzssss': INVENTOR EIMQW William E.Pa 1cala.

fi m (VM BY W,

I AT'roN Patented Dec. 2, 1941 IGNITBON WELDER CONTROL CIRCUITS William E. Pakala, Forest Hills, Pa., asslgnor to Westinghouse Electric 3; Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 16, 1940, Serial No. 319,284

15 Claims.

My invention relates to electric discharge apparatus and has particular relation to electric discharge systems performing the fimctions of high current contactors.

With the development of electric discharge valves. such as ignitrons, capable of carrying substantial current, the practice has arisen of using the discharge valves as high current contactors. In accordance with the teachings of the prior art the supply of alternating current from a source to a load, such as a welder, for example, is controlled by connecting a pair of ignitrons in antiparallel' between the load and the source and controlling the current flow through the igniters. In experimenting with apparatus of this type, I-have encountered considerable difficulty in controlling the igniter current. To directly open and close a connection between one or a plurality of igniters and the source is.

not practical where the rating is of the order of several hundred to several thousand amperes because the igniter current and potential required is substantial. Where the ignitrons are to carry several hundred amperes the igniter current required is of the order of 10. to 50 amperes and the potential is of the order of one hundred volts. The opening and closing of a circuit or this type engenders arcing at the interrupting contacts and the life of the circuit opening and closing controller is not sufllciently long for practical purposes.

It is accordingly an object of my invention to provide a non-arcing arrangement for initiating and discontinuing the firing current of a discharge valve rated to pass a load current of .the order of several hundred amperes.

Another object of my invention is to provide a system of simple structure for controlling the current flow through the firing electrodes of an ignitron circuit functioning as an alternating current contactor.

A more general object of my invention is to provide a readily variable impedance for controlling the current flow through a load that draws a large current of the order of 50 amperes intermittently.

More specifically stated, it is an object of my invention to provide a system of simple structure for supplying current from a source to a load that requires power in intermittent impulses.

My invention arises from the realization that the current flow through an ignitron maybe reliably controlled by an impedance in series with the igniter which can be varied abruptly over a sufllciently-wide range of values. To. merely vary the magnitude of an ordinary impedance does not suilice for the present purpose, since a sufllcient range" of variation for reliable firing cannot be achieved with the necessary speed. It often happens that the ignitrons in a contactor circuit should be rendered conductive or non-conductive within a half period of an ordinary 60-cycle alternating current source, and the corresponding variation to produce this condition should be correspondingly abrupt.

In accordance with my invention, the desired range of variation is attained by varying a reactance in circuit with igniter in such manner that it has at times the impedance of a parallel tuned circuit and at other times the impedance of a series tuned circuit. Since a parallel tuned circuit has substantial impedance the current flow through the igniter when it is interposed is small and the ignitron is non-conductive. A series tuned circuit has a small impedance and the current flow through an igniter when such a circuit is interposed may be sufllciently large to render the ignitron conductive. In accordance with my invention, the reactance in the igniter circuit is equivalent to a parallel circuit when the ignitron is to be non-conductive and a series tuned circuit when the ignitron is to be conductive. The reactance may be varied from one state to the other without mechanical contacts. Preferably the inductive reactance is provided with a coil, the reluctance of which is varied by inserting more or less magnetizable material in a gap. The same object may be achieved by varying the direct-current presaturation of the conductive reactances or by interposing more or less capacitive reactance.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with addi- ,tional objects and advantages thereof will best be understood from the following description of a specific embodiment when read in connection with'the accompanying drawing, in which the single figure is a diagrammatic view showing an embodiment of my invention.

In the drawing, my invention is illustrated in connection with a welding load comprising a welding transformer l across the secondary 3 of which a pair of welding electrodes 5 engaged with the work I, are connected. The welder is supplied from an alternating-current source 9 preferably of the usual commercial 60-cycle type. To control the current flow through the transformer l,- a pair of ignitrons II and it are interposed in anti-parallel between the source 0 and the primary II of the transformer. Each of the ignitrons has an anode II, a cathode l9 and an ignition electrode 2|.

In the practice of my invention, in its broader aspects, tubes of other types such as mercury pool tubes excited by the application of a high gap; the inductance is reduced and the network cifically, the ignitron with the immersed high resistivity ignition electrode has peculiar advantages and is to be preferred.

To control the current fiow through the'ignitrons II and I9, a reactive circuit is connected between the igniters 2| through a controller 29 which may be of the manual type such as a foot switch or a push button. The circuit comprises a plurality of capacitors 29 and 21 connected in series and an inductor 29 connected in parallel with one of the capacitors 25. The inductor is provided with a magnetizable core 99 having an air gap 9|. A non-magnetic disc 99 provided with peripheral inserts 99 of magnetizable material is mounted to be rotated by a synchronous motor 91 in such manner that the inserts successively pass through the gap. The inserts 95 are readily removable so that they may be arranged in any desired manner in the periphery of the disc. Preferably the number of spaces provided forinserts 95 in the periphery of the disc is so related to the speed oi the disc that one insert passes through the gap 9| during each half-period-of th source 9. The phase angle in the waves of the source when the inserts move into the gap is preset by a rheostat 99 in'the fiel circuit ll of the motor 91.

The inductor 29 has a magnitude such that with the controller 29 closed and with magnetizable insert in the gap 9|, the network 26--29 is tuned to the frequency of the source 9 and the current flow through the igniters 2| is negligible.

When no magntizable insert 95 is present in the 21-29 is tuned to the frequency of the source 9 and substantial current sufllcient for firing, flows through the igniters. To suppress deleterious current flow in an improper sense through the igniters during firing, rectifiers 49 and 45, prefrheostat 99 a non-magnetizable insert enters the gap 9| In such a case, the series tuned impedance 21--29 is interposed in the igniter circuit and substantial current fiows from the upper terminal of the source9 through the conductor 41,

the rectifier '99 associated with the right-hand valve l9, the series tuned network 21-29, the controller 29, the ignition electrode 2| and cathode |9 of the left-hand valve II, the primary II of the welding transformer to the lower terminal of the source. The current which flows through the ignition electrode and cathode of the-left-hand valve II is sufficient for firing and since the anode-cathode potential impressed on this valve is of the proper polarity, the valve is rendered conductive and current is supplied to the load The flow of current continues until the potential of the source 9 becomes sumciently negative to counteract the back electromotive force of the load and at this time, the left-hand ignitron is rendered non-conducive. Y, During the next half-period another non-magnetiaable insert may again reduce the magnitude of inductor 29 and in this case current flow through the ignition electrode 2| and cathode i9 possible.

29 is closed, the upper terminal of the source 9 is positive and the lower terminal is negative, and... I at a phase angle in the half-period preset by the ductive. The valves H and I 9 thus continue to supply current to the load in a manner predetermined by the arrangement of inserts in the disc 99 and the operation of controller 29.

Although I have shown and described a certain specific embodiment of my invention, 1 am fullyaware that many modifications thereof are My invention, therefore. is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination an electric discharge device having a control electrode and a plurality of principal electrodes, means for impressing potential between certain of said principal electrodes, a

source of periodically pulsating potential, means for connecting one terminal of said source to one .of said principal electrodes, reactance means for connecting said control electrode to another terminal of said source and means for varying said reactance means so that at times it constitutes a parallel circuit tuned to the frequency of said source and at other times it constitutes a series circuit tuned to the frequency of said source. 2. For use with a source of periodically pulsating potential an ignitron having a plurality of principal electrodes and an ignition electrode cooperative with one of said principal electrodes, means for impressing potential between certain of said principal electrodes, means for connecting said one principal electrode to a terminal of tion electrode cooperative with one of said principal electrodes, means for impressing potential between certain of said principal electrodes, means for connecting said one principal electrode to a terminal of said source, capacitive means interposed between said ignition electrode and an-. other terminal of said source, inductive means in parallel with a portion of said capacitive means and constituting therewith a parallel circuit tuned to the frequency of said source and means for at times varying said inductive means so that it forms a series tuned circuit tuned to the frequency of said source with the remainder of said capacitive means.

4. For use with a source of alternating current the combination comprising an ignitron having means for connecting said one principal electrode tca terminal of said source, capacitive means interposed between said ignition electrode and another terminal of said source, inductive means in parallel with a portion of said capacitive means and constituting therewith a parallel circuit tuned to the frequency of said source and reactive "means for at times varying said inductive means so-that it forms a series tuned circuit tuned to the frequency of said source with the of theright-hand valve l9 renders the latter con- '75 remainder of said capacitive means.

5. For use in varying current flow from a source of periodically pulsating current to a load the combination comprising capacitive means interposed between said source and said load, inductive means in circuit with said capacitive means and forming a parallel tuned circuit tuned to the frequency of said source with said capacitive means and means for varying said inductive means so that with said capacitive means it forms a series tuned circuit tuned to the frequency of said source.

6. The method of varying the current flow from a source of periodically pulsating current to a load with reactive means having a plurality of components interposed between said source and said load which comprises varying one of the components of said reactive means so that at prising inductive means in parallel with capacitive means tuned to the frequency of said source between said load and said source and at other times it interposes a series tuned circuit comprising said inductive means in series with capacitive means tuned to the frequency of said source between said load and said source.

7. For use in varying current flow from a source of periodically pulsating current to a load the combination comprising capacitive means interposed between said source and said load, inductive means in circuit with said capacitive means and forming a parallel tuned circuit tuned times it interposes a parallel tuned circuit comto the frequency of said source with said capacitive means and means for varying said inductive means so that it forms a series tuned circuit tuned to the frequency of said source, said varying means comprising a magnetic core having a gap and means for varying the reluctance of said gap.

8. For use in varying current flow from a source of periodically pulsatingcurrent to a load the combination comprising a plurality of capacitors interposed between said source and said load, inductive means in parallel with certain of said capacitors and forming a parallel tuned circuit tuned to the frequency of said source with said last-named capacitors and means for varying said inductive means so that it forms a series tuned circuit timed to the irequency of said source with the remainder of said capacitors.

9. For use in controlling the supply of current from an alternating current source to a load the combination comprising a pair of electric discharge valves each having an anode, a cathode and a control electrode interposed in anti-parallel between said source and said load, capacitive.

source and means for varying said reactive means so that it has substantially the impedance of a series tuned circuit tuned to the frequency of said source.

11. For use in controlling the supply of current from an alternating current source to a load the combination comprising a pair of electric discharge valves each having an anode, a cathode and a control electrode interposed in anti-parallel between said source and said load, a plurality of capacitors interconnecting said control electrodes, inductive means in parallel with certain 01' said capacitors and forming therewith a parallel tuned circuit tuned to the frequency of said source and means for varying said inductive means so that it forms with the remainder of said capacitors a series tuned circuit tuned to the frequency of said source.

12. For use in varying current flow from a source of periodically pulsating current to a load, the combination comprising capacitive means interposed between said source and said load, inductive means having a magnetizable core in circuit with said capacitive means and forming a parallel tuned circuit tuned to the frequency of said source with said capacitive means and means for varying said inductive means so that it forms a series tuned circuit tuned to the frequency of said source, said varying means comprising means for varying the reluctance of said core.

13. For use in varying current flow from a source of periodically pulsating current to a load, the combination comprising capacitive means interposed between said source and said load, inductive means having a magnetizable core with an air gap therein in circuit with said capacitive means and forming a parallel tuned circuit tuned to the frequency of said source with said capacitive means and means for varying said inductive means so that it forms a series tuned circuit tuned to the frequency of said source, said varying means comprising means for inserting magnetizable material in said gap.

14. For use in controlling the supply of current from an alternating-current source to a load, the combination comprising electric discharge means including a pair of cathodes, one of which is connected directly to one terminal of said source and the other or which is connected to another terminal of said source through said load, a control electrode associated with each said cathode,

means interconnecting said control electrodes, in-

- ductive means in circuit with said capacitive means and forming therewith a parallel tuned circuit tuned to the frequency of said source and means for varying said inductive means soreactive means interconnecting said control eleca parallel tuned circuit timed to the frequency of said source and means for varying said reactive means so that it has substantially the impedance of a series tuned circuit tuned to the frequency of said source.

15; The method of varying current flow from a. source of periodially pulsating current to a load with capacitive means interposed between said source and said lead, and inductive means in circuit with said capacitive means which comprises varying said inductive means so that at times it forms a parallel timed circuit tuned to the frequency of said source with a portion oi said capacitive means and at other times it forms a series tuned circuit tuned to the frequency of said source with another portion of said capacitive means.

. WILLIAM E. PAKALA. 

